Deoxyribonucleoside and deoxyribose catabolism in Bacillus subtilis

The Gram-positive soil bacterium Bacillus subtilis is able to use deoxyribonucleosides and deoxyribose as sole carbon and energy sources. After transport into the cell, deoxyribonucleosides are cleaved by nucleoside phosphorylases to deoxyribose-1-phosphate (dRib-1-P) and the respective pyrimidine or purine base. dRib-1-P can be converted to deoxyribose-5-phosphate (dRib-5-P) in a reaction catalyzed by phosphodeoxyribomutase. Finally, dRib-5-P is cleaved to acetaldehyde and glyceraldehyde-3-phosphate by the enzyme deoxyriboaldolase. After transportation into the cell deoxyribose is converted to dRib-5-P by deoxyribokinase. Synthesis of nucleoside phosphorylase, phosphodeoxyribomutase, deoxyriboaldolase and deoxyribokinase is increased when B. subtilis cells grow in the presence of deoxyribose or deoxyribonucleosides. In B. subtilis the dra, nupC and pdp genes, which encode deoxyriboaldolase, nucleoside uptake protein and pyrimidine nucleoside phosphorylase, respectively, are organized in an operon. Expression of both the dra-nupC-pdp operon is repressed by the repressor protein DeoR. Inactivation of DeoR results in constitutive expression of the respective genes. The operator sequence for the binding of DeoR to the regulatory region of the dra-nupC-pdp operon has been identified. It consists of a palindromic sequence upstream of the -35 region and of a repeated sequence between the -10 and -35 regions. We have now purified the DeoR protein and demonstrated that it binds tightly to it operator sequence in vitro. Addition of dRib-5-P to the assays releases the DeoR protein from the operator indicationg that dRib-5-P is the true inducer of DeoR control. The gene encoding doxyribokinase has been identified and it turned up to be the rbsK gene formerly thought to encode reibokinase, however, enzyme assays have revealed that rbsK encodes deoxyriborinase activity and not ribokinase activity.